diff -r 5973743a52a1 Lib/urllib/request.py
--- a/Lib/urllib/request.py	Sun Mar 06 18:10:58 2011 -0600
+++ b/Lib/urllib/request.py	Fri Apr 08 00:53:42 2011 +0300
@@ -811,14 +811,18 @@
             self.retried += 1
 
         if authreq:
-            mo = AbstractBasicAuthHandler.rx.search(authreq)
-            if mo:
-                scheme, quote, realm = mo.groups()
-                if scheme.lower() == 'basic':
+            scheme = authreq.split()[0]
+            if scheme.lower() == 'basic':
+                mo = AbstractBasicAuthHandler.rx.search(authreq)
+                if mo:
+                    scheme, quote, realm = mo.groups()
                     response = self.retry_http_basic_auth(host, req, realm)
                     if response and response.code != 401:
                         self.retried = 0
                     return response
+            else:
+                raise HTTPError(req.full_url, 401, "not basic auth: '%s'" % scheme,
+                                headers, None)
 
     def retry_http_basic_auth(self, host, req, realm):
         user, pw = self.passwd.find_user_password(realm, host)
@@ -904,6 +908,10 @@
             scheme = authreq.split()[0]
             if scheme.lower() == 'digest':
                 return self.retry_http_digest_auth(req, authreq)
+            else:
+                raise HTTPError(req.full_url, 401, "not digest auth: '%s'" % scheme,
+                                headers, None)
+
 
     def retry_http_digest_auth(self, req, auth):
         token, challenge = auth.split(' ', 1)